I have allergic reactions to a yellow colouring called annatto (in the US you might called it something else, or give it a number). Anyway, I heard that this colouring is made from Almonds, which is a common allergen. Has your child been tested for nut allergy?

I also as a child used to get wheezy when I drank orange cordial drinks - but I haven't bothered finding out about this since I can simply avoid this type of drink. I bet it has something to do with another yellow colouring though because it only happened witht he yellow drinks.